Dumbbell



FIG. 1 is a front elevational view of a dumbbell showing my new design, the rear view appearing the same as the front view;

FIG. 2 is a top plan view thereof, the bottom plan view appearing the same as the top view;

FIG. 3 is a side elevational view thereof, both sides appear the same; and,

FIG. 4 provides a perspective view thereof. 

The ornamental design for a dumbbell, as shown and described. 